1. Field of the Invention
The present invention relates to a seek routine of a hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. Each head is attached to a flexure arm to create a subassembly commonly referred to as a head gimbal assembly (“HGA”). The HGA's are suspended from an actuator arm. The actuator arm has a voice coil motor that can move the heads across the surfaces of the disks.
Information is typically stored in radial tracks that extend across the surface of each disk. Each track is typically divided into a number of segments or sectors. The voice coil motor and actuator arm can move the heads to different tracks of the disks.
FIG. 1 shows a typical track that has a number of fields associated with each sector. A sector may include an automatic gain control (“AGC”) field 1 that is used to adjust the strength of the read signal, a sync field 2 to establish a timing reference for the circuits of the drive, and ID 3 and Gray Code 4 fields to provide sector and track identification.
Each sector may have also a servo field 5 located adjacent to a data field 6. The servo field 5 contains a plurality of servo bits A, B, C and D that are read and utilized in a servo routine to position the head 7 relative to the track. By way of example, the servo routine may utilize the algorithm of ((A−B)−(C−D)) to create a position error signal (“PES”). The PES is used to create a drive signal for the voice coil motor to position the head on the track.
The drive will enter a seek routine to access data at different disk tracks. During a seek routine a requested address location is provided and a corresponding seek time and drive current is calculated to drive the voice coil motor and move the heads to the desired location. Before the head arrives at the desired disk location the seek routine enters a settle mode. In the settle mode the head velocity is reduced until the head reaches the desired track. The settle response time is dependent on the initial state when the seek routine enters the settle mode. The initial state includes the head velocity and the position of the head when the settle mode is initiated. The initial state can change depending on the head velocity, temperature and direction of head movement. The varying initial state can cause undesirable undershoot or overshoot settle behavior. It would be desirable to provide a scheme that compensates for changing initial states when a seek routine enters a settle mode.